1. Field of the Invention
This invention relates to a flux containing cored wire suitable for use in stainless steel welding, and more particularly to a flux cored wire which is applicable to welding operations in all positions under the same conditions including not only downhand, sideward, vertical and horizontal fillet welding operations but also overhead welding operations, and which is capable of forming a weld metal with excellent characteristics in terms of welding operation and X-ray property.
2. Prior Art
Because of handiness coupled with high efficiency and quality, the demand for flux cored wires (FCW) has been lately on a keen increase even in stainless steel welding processes. However, heretofore their applications have been restricted mostly to downhand and horizontal fillet welding operations and to part of welding operations in horizontal and vertical positions, finding almost no applications in operations in the overhead position.
More specifically, the stainless steels which have lower heat conductivity and solidification temperature as compared with carbon steels require higher welding techniques in the horizontal and vertical welding position which are more susceptible to dribbling of molten metal than the downhand welding position. Especially in the overhead welding, it has been difficult to obtain satisfactory X-ray property even by the use of specially designed power source and shielding gas.
Under these circumstances, various attempts have been made to meet the increasing demand for a flux cored wire which permits all-position welding. For example, flux cored wires of this sort are proposed in Japanese Patent Publication 59-15757 and Japanese Laid-Open Patent Application 59-212192.
The first mentioned Japanese Patent Publication 59-15757 describes a wire which is intended mainly for horizontal and vertical position welding, while the Japanese Laid-Open Patent Application 59-212192 discloses a flux cored wire which is applicable to welding operations in all of the downhand, horizontal and vertical positions although the welding condition differs greatly between the downhand and vertical positions. Besides, both of these prior art wires require low current welding condition in the vertical position as compared with the downhand position. Accordingly, in a case where a welding operation involves all welding positions in its sequence, it becomes necessary to use different wires in the downhand and vertical (or horizontal) positions or to use a wire under different conditions. More specifically, it becomes necessary to use in the vertical welding position a current which is about 50% lower than in the downhand welding position despite a material drop in efficiency, and the necessity of weaving makes it difficult to obtain beads with short legs, coupled with a problem that the wire is applicable only to plates having a thickness greater than 5 mm and not to plates of smaller thicknesses. In addition, in case of downward welding in the vertical position, the operation is often rendered infeasible by instable arc condition and dribbling of molten metal which destabilizes the molten pool.
Thus, owing to the problems arising in controlling welding operations or problems of efficiency in the vertical position welding, the conventional flux cored wires (FCW) have found only restricted applications, and therefore overhead welding operations have thus far relied on the covered arc welding or TIG welding without application of FCW.